Fuel Cell and Method of Forming the Same

ABSTRACT

In an embodiment, a fuel cell includes: a flexible substrate including a first fuel-tolerant material; a fitting on the flexible substrate, the fitting including first openings extending through an outer portion of the fitting; a primer coating on the outer portion of the fitting, the primer coating including a second fuel-tolerant material; first yarns strung through the first openings of the fitting, the first yarns stitched into the flexible substrate; and an encapsulant encapsulating the first yarns, the primer coating, and the outer portion of the fitting, the encapsulant disposed on the flexible substrate, the encapsulant including a third fuel-tolerant material, the third fuel-tolerant material chemically bonded to the second fuel-tolerant material and the first fuel-tolerant material.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a divisional of U.S. patent application Ser. No.17/578,134, filed on Jan. 18, 2022, entitled “Fuel Cell and Method ofForming the Same,” which is incorporated herein by reference in itsentirety.

BACKGROUND

Vehicles such as cars, aircraft, and the like typically include a fuelsystem. A fuel system includes components for delivering fuel to anengine of the vehicle. As the demand for fuel efficient vehicles hasincreased, additional problems in fuel systems arise that should beaddressed. Some types of aircraft present particular challenges to theincreasing of fuel efficiency.

SUMMARY

In an embodiment, a fuel cell includes: a flexible substrate including afirst fuel-tolerant material; a fitting on the flexible substrate, thefitting including first openings extending through an outer portion ofthe fitting; a primer coating on the outer portion of the fitting, theprimer coating including a second fuel-tolerant material; first yarnsstrung through the first openings of the fitting, the first yarnsstitched into the flexible substrate; and an encapsulant encapsulatingthe first yarns, the primer coating, and the outer portion of thefitting, the encapsulant disposed on the flexible substrate, theencapsulant including a third fuel-tolerant material, the thirdfuel-tolerant material chemically bonded to the second fuel-tolerantmaterial and the first fuel-tolerant material. In some embodiments, thefuel cell further includes: second yarns stitched into the flexiblesubstrate and over the first yarns, the encapsulant encapsulating atleast some of the second yarns. In some embodiments of the fuel cell,the first fuel-tolerant material and the second fuel-tolerant materialare polyvinylidene fluoride, and the third fuel-tolerant material is apolyurethane resin. In some embodiments of the fuel cell, the firstyarns are bicomponent yarns including a core and a sheath. In someembodiments of the fuel cell, the sheath includes a bicomponent filamenthaving a melting point in a range of 50° C. to 200° C. In someembodiments of the fuel cell, bundles of the first yarns are threadedthrough respective ones of the first openings of the fitting, the firstyarns of the bundles radiating from the first openings. In someembodiments of the fuel cell, the first yarns of the bundles curve in afirst direction as the first yarns radiate from the first openings. Insome embodiments of the fuel cell, the first yarns of the bundles fanout as the first yarns radiate from the first openings. In someembodiments of the fuel cell, the fitting includes a second openingextending through an inner portion of the fitting, the inner portion ofthe fitting not covered by the encapsulant.

In an embodiment, a rotorcraft includes: a rigid fuel line; and aflexible fuel cell connected to the rigid fuel line, the flexible fuelcell including: a flexible substrate; a fitting on the flexiblesubstrate; yarns attaching the fitting to the flexible substrate; and anencapsulant encapsulating the yarns and an outer portion of the fitting,the encapsulant bonded to the flexible substrate, the rigid fuel lineextending through the encapsulant, the fitting, and the flexiblesubstrate. In some embodiments, the rotorcraft further includes: anengine connected to the rigid fuel line. In some embodiments of therotorcraft, the rigid fuel line is line for refueling the flexible fuelcell. In some embodiments of the rotorcraft, the flexible fuel cellfurther includes: a primer coating on the outer portion of the fitting,the encapsulant bonded to the primer coating. In some embodiments of therotorcraft, the yarns are strung through the outer portion of thefitting and are stitched into the flexible substrate.

In an embodiment, a method includes: placing a first rigid fitting and asecond rigid fitting on a first flexible substrate and a second flexiblesubstrate, respectively, the first rigid fitting including firstopenings extending through a first outer portion of the first fitting,the second rigid fitting including second openings extending through asecond outer portion of the second fitting; stitching first yarnsthrough the first openings and into the first flexible substrate with anembroidering machine, the embroidering machine controlled according to afirst computer numerical control process; stitching second yarns throughthe second openings and into the second flexible substrate with theembroidering machine, the embroidering machine controlled according to asecond computer numerical control process, the second computer numericalcontrol process different from the first computer numerical controlprocess; and encapsulating the first yarns, the second yarns, the firstrigid fitting, and the second rigid fitting with an encapsulant, theencapsulant extending through the first openings and the secondopenings. In some embodiments of the method, the first yarns form afirst semi-rigid attachment structure for the first rigid fitting, andthe second yarns form a second semi-rigid attachment structure for thesecond rigid fitting, the method further including: selecting the firstcomputer numerical control process according to a first strength of thefirst semi-rigid attachment structure; and selecting the second computernumerical control process according to a second strength of the secondsemi-rigid attachment structure, the second strength different from thefirst strength. In some embodiments of the method, the first rigidfitting and the first flexible substrate form a first fitting patch, thesecond rigid fitting and the second flexible substrate form a secondfitting patch, and the method further includes: attaching the firstfitting patch to a first side of a flexible fuel cell body; andattaching the second fitting patch to a second side of the flexible fuelcell body. In some embodiments of the method, the first rigid fitting issmaller than the second rigid fitting. In some embodiments, the methodfurther includes: forming a first primer coating on the first outerportion of the first fitting; and forming a second primer coating on thesecond outer portion of the second fitting. In some embodiments of themethod, the first yarns and the second yarns include a filamentcomponent having a melting point, the encapsulant includes apolyurethane resin formulated from isocyanate and polyol, and thepolyurethane resin is formulated at a temperature lower than the meltingpoint of the filament component.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIGS. 1A-1B are schematic views of a rotorcraft, in accordance with someembodiments;

FIGS. 2A-2B are schematic views of a fuel cell assembly for arotorcraft, in accordance with some embodiments;

FIGS. 3A-3B are detailed views of a fitting for a fuel cell, inaccordance with some embodiments;

FIG. 4 is a detailed view of a portion of a fuel cell, in accordancewith some embodiments;

FIGS. 5A-5D are views of intermediate stages in the manufacturing of afuel cell, in accordance with some embodiments;

FIG. 6 is a flow diagram of a method for manufacturing a fuel cell, inaccordance with some embodiments;

FIG. 7 is a flow diagram of a method for manufacturing a fuel cell, inaccordance with some embodiments; and

FIGS. 8A-8B are detailed views of a fitting for a fuel cell, inaccordance with some other embodiments.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Illustrative embodiments of the system and method of the presentdisclosure are described below. In the interest of clarity, all featuresof an actual implementation may not be described in this specification.It will of course be appreciated that in the development of any suchactual embodiment, numerous implementation-specific decisions may bemade to achieve the developer's specific goals, such as compliance withsystem-related and business-related constraints, which will vary fromone implementation to another. Moreover, it should be appreciated thatsuch a development effort might be complex and time-consuming but wouldnevertheless be a routine undertaking for those of ordinary skill in theart having the benefit of this disclosure.

Reference may be made herein to the spatial relationships betweenvarious components and to the spatial orientation of various aspects ofcomponents as the devices are depicted in the attached drawings.However, as will be recognized by those skilled in the art after acomplete reading of the present disclosure, the devices, members,apparatuses, etc. described herein may be positioned in any desiredorientation. Thus, the use of terms such as “above,” “below,” “upper,”“lower,” or other like terms to describe a spatial relationship betweenvarious components or to describe the spatial orientation of aspects ofsuch components should be understood to describe a relative relationshipbetween the components or a spatial orientation of aspects of suchcomponents, respectively, as the device described herein may be orientedin any desired direction.

According to various embodiments, a fuel cell for a vehicle is formedwith a flexible fuel cell body. Fittings for rigid fuel lines areattached to the flexible fuel cell body with semi-rigid attachmentstructures. The semi-rigid attachment structures are more rigid than theflexible fuel cell body and are less rigid than the fittings and thefuel lines. This allows the semi-rigid attachment structures to bufferstress, reducing the risk of damage at the point where the rigid fuelline is mated to the flexible fuel cell body. Further, the semi-rigidattachment structures are formed by a computer numerical control (CNC)process which can be performed with high precision and repeatability.Less material may be used when forming the semi-rigid attachmentstructures, thereby reducing the weight of the resulting fuel cell.

FIGS. 1A-1B are schematic views of a rotorcraft 10, in accordance withsome embodiments. The rotorcraft 10 includes a main rotor hub assembly12, which is rotatable relative to a fuselage 16 of the rotorcraft 10.The main rotor hub assembly 12 includes main rotor blades 14. The pitchof the main rotor blades 14 can be collectively and/or cyclicallymanipulated to selectively control direction, thrust, and lift of therotorcraft 10. A tailboom 20 extends from the fuselage 16, and a tailrotor hub assembly 24 is attached to an aft portion of the tailboom 20.The tail rotor hub assembly 24 includes a tail rotor 22, which isrotatable relative to the tailboom 20. The tail rotor 22 maycollectively provide thrust in the opposite direction as the rotation ofthe main rotor hub assembly 12, so as to counter torque effects createdby the main rotor blades 14.

The components of the rotorcraft 10 (e.g., the main rotor hub assembly12 and the tail rotor hub assembly 24) are powered by one or moreengines 30. For example, the engines 30 may power the main rotor hubassembly 12 via a main rotor gearbox 32. The engines 30 may also powerother components (not separately illustrated), such as alternators,cooling units, or the like. The rotorcraft 10 further includes a fuelsystem 40, which includes a fuel cell assembly 42. The fuel cellassembly 42 may be located in a lower portion of the fuselage 16. Thefuel cell assembly 42 is coupled to the fuselage 16, and may be fully orpartially integral with the fuselage 16, or may be an independentcomponent which is secured to the fuselage 16. The fuel cell assembly 42may be located elsewhere in the rotorcraft 10. The fuel cell assembly 42includes one or more the fuel cells 44 for storing fuel. The fuelcontained in the fuel cells 44 is used as an energy source to power thevarious systems of the rotorcraft 10 such as the main rotor hub assembly12 and the tail rotor hub assembly 24. Specifically, the fuel system 40is operable to deliver fuel stored in the fuel cells 44 to the engines30. The fuel cells 44 may be fluidly coupled to components of therotorcraft 10, such as the engines 30, with one or more fuel lines 46.The fuel lines 46 are hoses formed of a rigid material, such as a metal,such as aluminum, steel, or the like.

FIGS. 2A-2B are schematic views of a fuel cell assembly 42 for arotorcraft, in accordance with some embodiments. As previously noted,the fuel cell assembly 42 includes one or more the fuel cells 44 forstoring fuel. The fuel cells 44 may be fluidly coupled to one another toallow for the transfer of fuel therebetween. Each fuel cell 44 includesa flexible body 48 and one or more fittings 50. As will be subsequentlydescribed in greater detail, the fuel cells 44 also include semi-rigidattachment structures (not illustrated in FIGS. 2A-2B, but see FIG. 4 )which attach the fittings 50 to the flexible bodies 48.

Each flexible body 48 is formed of one or more layers of flexiblematerials, such as fabric and/or composite materials, so that fuel cell44 is a flexible fuel bag or fuel bladder. Flexible fuel cell bodies aremore resistant to ballistic projectiles than rigid fuel cell bodies,which may be advantageous when the rotorcraft is utilized in militaryapplications. For example puncturing of the fuel cells 44 duringoperation may result in a loss of fuel supply to the components of therotorcraft. In some embodiments, the flexible body 48 includes an innerlayer, an outer layer around the inner layer, and a middle layer betweenthe outer layer and the inner layer. The inner layer may be formed of afuel-tolerant material such as polyvinylidene fluoride, nylon, urethane,or the like. Any material which is substantially inert to fuel may beutilized for the inner layer. The outer layer may be formed of apuncture-resistant material such as a metal or metal alloy. Any materialwhich is substantially resistant to being pierced may be utilized forthe outer layer. The middle layer may be formed of a self-healing gel,such as an elastomeric gel. Any material which is capable of expandingto self-seal holes (e.g., ballistically formed holes) in the flexiblebody 48 may be utilized for the middle layer. The flexible body 48 isdefined by multiple sides, including a top side 48A, a bottom side 48B,a forward side 48C, an aft side 48D, a port side 48E, and a starboardside 48F. However, it should be appreciated that the flexible body 48may have any number of curved or straight sides, which each face anydesired direction. Each of the fuel cells 44 may have different shapes,as shown, or may have the same shape.

The fittings 50 are attached to the flexible bodies 48, and are part ofinlets/outlets for the fuel cells 44. Fuel may be added to or removedfrom a fuel cell 44 through a fitting 50 and a fuel line 46 (see FIG.1A) which is connected to the fitting 50. The fuel lines 46 connected tothe fittings 50 may be fuel lines for delivering fuel to the components(e.g., engines) of the rotorcraft, fuel lines for refueling the fuelcells 44, or the like. As previously noted, the fuel lines 46 are rigid.The fittings 50 are also formed of a rigid material. Acceptable rigidmaterials for the fittings 50 include metals such as aluminum, steel, orthe like; composite materials such as a stack-up of a carbon fiberreinforcement fabric within a fuel resistant 2K urethane matrix; or thelike. In some embodiments, the fuel lines 46 and the fittings 50 areformed of the same rigid material. The fittings 50 may function asmating points where the rigid fuel lines 46 connect to the flexiblebodies 48 of the fuel cells 44. The fuel lines 46 and the fittings 50are more rigid than the flexible bodies 48. Some of the fittings 50 mayalso be utilized to fluidly coupled the fuel cells 44 to one another.The fittings 50 are ring-shaped.

The fuel cells 44 may have any desired quantity of fittings 50. In someembodiments, the fuel cells 44 have from six to eight fittings 50.Further, the fuel cells 44 may have different shapes and/or sizes offittings 50. For example, a fuel cell 44 may have a first fitting 50, ofa first size and/or shape for refueling the fuel cell 44, and may have asecond fitting 502 of a different second size and/or shape fordelivering fuel to the components of the rotorcraft from the fuel cell44. Further, although the fittings 50 are shown in FIGS. 2A-2B as havinga stadium ring shape, the fittings 50 may have any acceptable ringshape. For example, and as will be subsequently described for FIGS.3A-3B, the fittings 50 may have a circular ring shape.

FIGS. 3A-3B are detailed views of a fitting 50 for a fuel cell, inaccordance with some embodiments. As previously noted, the fitting 50has a ring shape. In this embodiment, the fitting 50 has a circular ringshape, such that the fitting 50 is an annulus. The fitting 50 is definedby an inner sidewall 50A an outer sidewall 50B. The inner sidewall 50Ais a sidewall of an inner portion of the fitting 50, and the outersidewall 50B is a sidewall of an outer portion of the fitting 50. Theinner sidewall 50A defines a first opening 52, which extends through thecenter of the fitting 50. During operation, fuel flows through the firstopening 52 for ingress to and egress from the fuel cell. The outersidewall 50B defines the edge of the fitting 50. In some embodiments,the fitting 50 is a single continuous rigid material which extends fromthe inner sidewall 50A to the outer sidewall 50B. In some embodiments,the inner portion of the fitting 50 includes a raised portion 50R, andthe inner sidewall 50A includes a sidewall of the raised portion 50R.The raised portion 50R is raised from a top surface of the fitting 50.

A plurality of second openings 54 are disposed around the first opening52. The second openings 54 extend through the fitting 50. The secondopenings 54 are in the outer portion of the fitting 50, such that theyare closer to the outer sidewall 50B than to the inner sidewall 50A. Aswill be subsequently described in greater detail, semi-rigid attachmentstructures (not illustrated in FIGS. 3A-3B, but see FIG. 4 ) will beformed in the second openings 54 to attach the fittings 50 to a flexiblefuel cell body.

Optionally, a primer coating 56 is on the outer portion of the fitting50. The primer coating 56 is on the outer sidewall 50B of the fitting50, and is on top and bottom surfaces of the outer portion of thefitting 50. The inner sidewall 50A of the fitting 50 and the top andbottom surfaces of the inner portion of the fitting 50 are free of theprimer coating 56. The primer coating 56 may be formed of afuel-tolerant material such as polyvinylidene fluoride, nylon, urethane,or the like, which is capable of adhering to the fitting 50. Anymaterial which is substantially inert to fuel may be utilized for theprimer coating 56. In some embodiments, the primer coating 56 includesthe same fuel-tolerant material as the outer layer of the flexible body48 of the fuel cell 44 (see FIGS. 2A-2B).

As will be subsequently described in greater detail, the material of theprimer coating 56 is capable of forming strong chemical bonds with anencapsulant 66 (see below, FIG. 4 ) that will be subsequently used toencapsulate the outer portion of the fitting 50, thereby increasingadhesive strength of the encapsulant 66. For example, the adhesivestrength of the encapsulant 66 without the primer coating 56 may be lessthan about 20 pounds per linear inch, and the adhesive strength of theencapsulant 66 with the primer coating 56 may be greater than about 100pounds per linear inch. When the encapsulant 66 is formed of aurethane-based resin, the primer coating 56 is formed of a material thatis co-attachable to the fitting 50 and the encapsulant 66.

FIG. 4 is a detailed view of a portion of a fuel cell 44, in accordancewith some embodiments. A fitting 50, a flexible substrate 70, and anattachment structure 60 for the fitting 50 and the flexible substrate 70are shown. The attachment structure 60 includes a plurality of mainyarns 62, plurality of support yarns 64, and an encapsulant 66 (shown inghost for clarity of illustration). The flexible substrate 70 may beformed of a similar fuel-tolerant material as the outer layer of theflexible body 48. As will be subsequently described in greater detail,the flexible substrate 70 will be subsequently attached to the flexiblebody 48.

The fuel cell 44 is flexible so that it may deform without cracking inresponse to external stress. If fuel lines (which are rigid) wereconnected directly to the fuel cell 44 (which is flexible), there wouldbe discontinuous transition in rigidity at the connecting point. Thisdiscontinuous transition presents a high risk of failure. The attachmentstructure 60 serves as a transition in rigidity at the connecting pointfor the fuel lines. The attachment structure 60 is semi-rigid, beingmore rigid than the flexible body 48 and less rigid than the fuel linesand the fitting 50. Specifically, the attachment structure 60 isflexible enough to undergo some deformation responsive to externalstress, but is rigid enough to spring back to its original positionafter the external stress is removed. In other words, the attachmentstructure 60 is capable of acting as a buffer for stress, helping reducethe risk of the rigid fuel line cutting, tearing, or shearing theflexible body 48 when stress is exerted on the fuel cell 44. Theformation of voids around the attachment structure 60 during deformationmay thus be avoided, reducing the risk of leaks from the fuel cell 44.

The main yarns 62 are strung through the second openings 54 and arestitched into the flexible substrate 70, thereby securing the outerportion of the fitting 50 to the flexible substrate 70. The main yarns62 are high tenacity yarns which are capable of withstanding largeforces. The main yarns 62 may be formed of polyester, a 100-denierultra-high-molecular-weight polyethylene (UHMWPE) filament thread havinga tenacity of at least 30 grams per denier, a 150-denier high-tenacitypolyester yarn having a tenacity of at least 7.5 grams per denier, orthe like. In some embodiments, the main yarns 62 are bicomponent yarns,e.g., yarns including a core of a first filament component and a sheathof a second filament component. The core may have a higher tenacity thanthe sheath, and the sheath may have a lower melting point than the core.In some embodiments, the sheath is a bicomponent filament having a lowmelting point, such as a temperature in the range of 50° C. to 200° C.For example, the bicomponent filament with a low melting point may be aUHMWPE. The main yarns 62 are grouped into bundles 68 (including bundles68A, 68B, 68C), with each respective bundle 68 being threaded through arespective one of the second openings 54. The main yarns 62 of eachrespective bundle 68 radiate from their respective second opening 54,and fan out as they radiate from the respective second opening 54. Insome embodiments, the ends of the main yarns 62 in each bundle 68 (e.g.,the ends distal the fitting 50) are separated by the same distance. Themain yarns 62 may (or may not) curve as they radiate from the fitting50. In various embodiments, the main yarns 62 may curve in the samedirection (as illustrated), may curve in different directions, or may bestraight.

The strength of the attachment structure 60 is determined by severalproperties of the main yarns 62. The tenacity of the main yarns 62contributes to the strength of the attachment structure 60, with alarger tenacity resulting in a stronger attachment structure. In someembodiments, the main yarns 62 have a tenacity in the range of 30 gramsbreaking force per denier to 40 grams breaking force per denier. Theareal density of the main yarns 62 (e.g., on the surface of the flexiblesubstrate 70) also contributes to the strength of the attachmentstructure 60, with a larger areal density resulting in a strongerattachment structure. In some embodiments, the main yarns 62 have anareal density in the range of 3 per cm² to 50 per cm². The length of themain yarns 62 (e.g., the length the yarns 62 radiate from the fitting50) also contributes to the strength of the attachment structure 60,with a larger length resulting in a stronger attachment structure. Insome embodiments, the main yarns 62 have a length in the range of 7 cmto 70 cm. The radius of curvature of the main yarns 62 also contributesto the strength of the attachment structure 60, with a larger radius ofcurvature resulting in a stronger attachment structure. In someembodiments, the main yarns 62 have a radius of curvature (e.g., arclength) in the range of 11 cm to 16 cm. The main yarns 62 may have thesame or different tenacities; the same or different densities; the sameor different lengths; or the same or different radii of curvature.Although these properties of the main yarns 62 contribute to thestrength of the attachment structure 60, they also contribute to themass of the attachment structure 60. As will be subsequently describedin greater detail, when the attachment structure 60 is formed, thetenacity, areal density, length, and radius of curvature of the mainyarns 62 is selected to obtain a desired strength while maintaining adesired mass.

The support yarns 64 are stitched into the flexible substrate 70 andover the main yarns 62, thereby helping secure the main yarns 62 to theflexible substrate 70. The support yarns 64 extend at least partiallyaround the fitting 50, such that each support yarn 64 crosses aplurality of the main yarns 62. The support yarns 64 may be formed ofthe same fibers as the main yarns 62, or may include different fibersthan the main yarns 62.

The encapsulant 66 encapsulates the outer portion of the fitting 50, atleast a portion of each main yarn 62, and at least some of the supportyarns 64. The encapsulant 66 covers the outer portion of the fitting 50where the main yarns 62 are strung through the second openings 54, andalso covers at least a portion of the primer coating 56. An innerportion of the fitting 50 is not covered by the encapsulant 66, so thata rigid surface of the fitting 50 may be exposed for subsequentconnection to a fuel line. The encapsulant 66 further covers someportions of the flexible substrate 70, e.g., the portions between theyarns 62, 64. Further, the encapsulant 66 fills the remaining portionsof the second openings 54 which are not filled by the main yarns 62. Theencapsulant 66 is formed of a fuel-tolerant material such as apolyurethane resin. The fuel-tolerant material of the encapsulant 66 iscapable of forming strong chemical bonds with the fuel-tolerantmaterial(s) of the primer coating 56 and the substrate 70. The materialof the encapsulant 66 may be different from the material(s) of theprimer coating 56 and the substrate 70. The fuel-tolerant material ofthe encapsulant 66 may also be capable of forming strong chemical bondswith the material(s) of the yarns 62, 64.

FIGS. 5A-5D are views of intermediate stages in the manufacturing of afuel cell 44, in accordance with some embodiments. FIGS. 5A-5D arecross-sectional views of a portion of a fuel cell 44 along a similarcross-section as reference cross-section 5-5′ in FIG. 2B, and show theformation of an attachment structure 60. The attachment of a singlefitting 50 to a flexible body 48 is illustrated. As will be subsequentlydescribed in greater detail, multiple fittings 50 may be attached to aflexible body 48. FIG. 6 is a flow diagram of a method 600 formanufacturing a fuel cell 44, and is described with FIGS. 5A-5D.

In FIG. 5A and step 602, a flexible substrate 70 and a fitting 50 arereceived or formed. The fitting 50 may be formed by milling a metal orcomposite material. The milling may be controlled using a CNC process.In embodiments where a primer coating 56 is on the fitting 50, theprimer coating 56 may be formed by treating the outer portions of thefitting 50 with a polymeric plasma coating process. An opening 78 isformed in the flexible substrate 70. The opening 78 may be formed bycutting the flexible substrate 70 using the fitting 50 as a stencil.

In FIG. 5B and step 604, the fitting 50 is attached to the flexiblesubstrate 70. Attaching the fitting 50 to the flexible substrate 70includes placing the fitting 50 on the flexible substrate 70 so that theraised portion 50R (see FIGS. 3A-3B) of the fitting 50 extends throughthe opening 78, and then attaching the outer portion of the fitting 50to the flexible substrate 70 with the yarns 62, 64. In embodiments wherethe primer coating 56 is present, the primer coating 56 contacts theouter surface of the flexible substrate 70. In embodiments where theprimer coating 56 is omitted, the fitting 50 contacts the outer surfaceof the flexible substrate 70.

The outer portion of the fitting 50 is attached to the flexiblesubstrate 70 by stitching the main yarns 62 through the second openings54 and into the flexible substrate 70. The support yarns 64 are thenstitched over the main yarns 62 and into the flexible substrate 70. Theyarns 62, 64 may be stitched into the flexible substrate 70 using anembroidering machine such as a JGW-0100-650 Technical EmbroideringMachine from ZSK. The stitching is controlled using a CNC process, whichdetermines the placement of the yarns 62, 64. Utilizing a CNC processimproves the accuracy and repeatability of the stitching, especiallywhen compared to manual stitching. Manufacturing yield rates may thus beimproved. The CNC process is one which is capable of controlling thestitching (e.g., needle movement) in three directions (e.g., X-axis,Y-axis, and Z-axis). Controlling the stitching along the Z-axis allowsthe yarns 62 to be threaded through the second openings 54 even when thefitting 50 has a large thickness. The stitching may be performed byprogramming the CNC process for the embroidering machine, and thenperforming the stitching with the embroidering machine controlled usingthe CNC process. The CNC process programming may be performed using,e.g., EPCWin from ZSK. As will be subsequently described in greaterdetail, the CNC process is programmed according to the desired strengthof the resulting attachment structure 60. Achieving a desired density,length, and radius of curvature for the main yarns 62 is easier with aCNC process than manual stitching, as CNC processes are less prone toerror than manual stitching. As such, the stitching may be performedwith a smaller margin of error, and so less of the yarns 62, 64 may beused while still achieving the desired density, length, and radius ofcurvature. The weight of the fuel cell 44 may thus be reduced, which isparticularly advantageous when the fuel cell 44 is utilized for anaircraft.

In FIG. 5C and step 606, the encapsulant 66 is formed amongst the yarns62, 64, the fitting 50, and the flexible substrate 70. Specifically, theencapsulant 66 is formed around the outer portion of the fitting 50, atleast a portion of each main yarn 62, and at least some of the supportyarns 64. The encapsulant 66 may also be formed on at least a portion ofthe primer coating 56 and the outer surface of the flexible substrate70. The encapsulant 66 is not formed in the openings 52, 78, so thatthey remain unobstructed. The encapsulant 66 may be formed bycompression molding, injection molding, or the like. In someembodiments, the mold is an aluminum mold, and the molding process isperformed at a vacuum, which can help avoid the formation of voids inthe encapsulant 66, such as voids in the second openings 54 or voidsaround the yarns 62, 64. An opening 80 extends through the encapsulant66. The opening 80 exposes the inner portion of the fitting 50, and isaligned with the openings 52, 78. In the illustrated embodiment, theencapsulant 66 covers all of the primer coating 56. In anotherembodiment, the encapsulant 66 covers a portion of the primer coating56. The encapsulant 66 is also formed in any spaces between the fitting50 and the flexible substrate 70.

In some embodiments where the yarns 62, 64 are bicomponent yarns havinga sheath with a low melting point, the molding process for theencapsulant 66 is a cold chemistry process. For example, the encapsulant66 may be a polyurethane resin formulated from isocyanate and polyol.The isocyanate may be methylene diphenyl diisocyanate and the polyol maybe a polyether. The molding process for the encapsulant 66 is performedat a temperature which is lower than the melting point of the sheath ofthe yarns 62, 64. In some embodiments, the molding process is performedat a temperature in the range of 20° C. to 100° C. A curing process(e.g., vulcanization process) for the encapsulant 66 may thus be omittedfrom the molding process, decreasing processing time. During formation,the material of the encapsulant 66 forms strong chemical bonds (such ascovalent bonds) with the material(s) of the primer coating 56 and theflexible substrate 70. Thus, the fuel-tolerant material of theencapsulant 66 is chemically bonded to the fuel-tolerant material of theprimer coating 56 and the fuel-tolerant material of the flexiblesubstrate 70. The strength of the resulting attachment structure 60 maythus be improved. The flexible substrate 70, the encapsulant 66, theyarns 62, 64, and the fitting 50 collectively form a fitting patch,which is a pre-formed fitting patch for a fuel cell 44.

The openings 52, 78, 80 collectively define an opening 82. The opening82 extends through the fitting patch (e.g., through the encapsulant 66,the fitting 50, and the flexible substrate 70). As such, the opening 82defines an inlet/outlet for the fuel cell 44. A rigid fuel line (e.g.,the fuel line 46; see FIG. 1A) extends through the opening 82.

In FIG. 5D and step 608, the fitting patch (including the encapsulant66, the yarns 62, 64, the flexible substrate 70, and the fitting 50) isattached to a flexible body 48 for a fuel cell 44. As previously noted,the flexible body 48 includes an inner layer 72, a middle layer 74, andan outer layer 76. In some embodiments, the fitting patch is attached tothe flexible body 48 such that it is disposed between the middle layer74 and the outer layer 76. When the flexible body 48 is formed of layersof composite materials, the various layers may be laminated on eachother and on the fitting patch.

As previously noted, the fuel cells 44 may have any desired quantity offittings 50. Each of the fittings 50 may be attached to a flexible body48 using a similar process as previously described for FIGS. 5A-5D and 6. The attachment structures 60 may be formed to have differentstrengths, as called for by the design of a fuel cell 44. For example, afirst attachment structure 60 may be in a high-stress region of a fuelcell 44 and may be formed to have a greater strength, while a secondattachment structure 60 may be in a low-stress region of the fuel cell44 and may be formed to have a lesser strength. Referring back to FIGS.2A-2B, a fitting 50 at the top side 48A or the bottom side 48B of aflexible body 48 may be subject to lower stresses than a fitting 50 atthe forward side 48C, aft side 48D, port side 48E, and starboard side48F of the flexible body 48. More generally, fitting 50 at larger sidesof a flexible body 48 may be subject to lower stresses than fittings 50at smaller sides of a flexible body 48. Further, smaller fittings 50 maybe subject to lower stresses than larger fittings 50.

The strength of an attachment structure 60 may be controlled byadjusting the density, length, and radius of curvature for the mainyarns 62 of the attachment structure 60. Those properties for the mainyarns 62 may be adjusted by programming a CNC process for theembroidering machine in accordance with those properties. For example,to form a first attachment structure 60 when a greater strength isdesired, a first CNC process for the embroidering machine may beprogrammed so that the embroidering machine stitches the main yarns 62for the first attachment structure 60 with a large density, largelength, and/or large radius of curvature. Similarly, to form a secondattachment structure 60 when a lesser strength is desired, a second CNCprocess for the embroidering machine may be programmed so that theembroidering machine stitches the main yarns 62 for the secondattachment structure 60 with a small density, small length, and/or smallradius of curvature. Programming a CNC process may include modelling thestress that an attachment structure 60 will undergo during operation,and selecting the density, length, and radius of curvature for the mainyarns 62 which will produce a strong enough attachment structure towithstand that stress. In some embodiments, the CNC process for theembroidering machine is selected from a lookup table in which thedensity, length, and radius of curvature for yarns are indexed accordingto the desired strength of the resulting attachment structure.

As previously noted, stronger attachment structures have a larger mass.In some embodiments, each attachment structure 60 is formed to have astrength that is sufficient for its design, but is not excessivelylarger than the strength called for by the design. Accordingly, eachattachment structure 60 may be formed to a sufficient strength withoutexcessively increasing the mass of the fuel cell 44. Controlling thestitching of the main yarns 62 with a CNC process allows the strength ofeach attachment structure 60 to be more precisely controlled than manualstitching, allowing for a larger degree of optimization when balancingstrength and mass.

Other properties may also contribute to the strength of the attachmentstructure 60. The quantity of second openings 54 in the fittings 50 alsocontributes to the strength of the attachment structure 60, with alarger quantity of second openings 54 resulting in a stronger attachmentstructure. In some embodiments, the quantity of second openings 54 inthe fittings 50 is also determined according to the desired strength ofthe resulting attachment structure.

In some embodiments, the process previously described for FIGS. 5A-5Dand 6 may be utilized to manufacture a pre-formed fitting patch for afuel cell 44, in lieu of manufacturing an entire fuel cell 44. Forexample, step 608 may be omitted, thereby forming a fitting patch havinga pre-attached fitting 50. The pre-formed fitting patch may then bestored and subsequently utilized to repair a damaged fuel cell 44 ormanufacture a new fuel cell 44. For example, a damaged fitting 50 may beremoved from the flexible body 48 of a fuel cell 44, and a pre-formedfitting patch having a pre-attached fitting 50 may then be attached tothe flexible body 48 of the fuel cell 44, thereby replacing the damagedfitting 50.

Some variations of the process previously described for FIGS. 5A-5D and6 are contemplated. For example, the flexible substrate 70 may beomitted, and instead a fitting 50 may be directly attached to a flexiblebody 48 of a fuel cell 44. In such an embodiment, a similar process asdescribed for steps 602-606 may be performed using the flexible body 48in lieu of the flexible substrate 70.

FIG. 7 is a flow diagram of a method 700 for manufacturing a fuel cell44, in accordance with some embodiments. The method 700 is performed toattach multiple fittings 50 to a flexible body. The method 700 isdescribed in conjunction with reference to the features illustrated inFIGS. 2A-4 .

In step 702, a first rigid fitting 50 and a second rigid fitting 50 areplaced on a first flexible substrate 70 and a second flexible substrate70. The first rigid fitting 50 includes openings 54 extending through anouter portion of the first fitting 50. The second rigid fitting 50includes openings 54 extending through an outer portion of the secondfitting 50. The first rigid fitting 50 may be smaller than the secondrigid fitting 50.

In step 704, first main yarns 62 are stitched through the openings 54 ofthe first rigid fitting 50 and into the first flexible substrate 70 withan embroidering machine. The embroidering machine is controlledaccording to a first computer numerical control process. The firstcomputer numerical control process may be selected according to adesired strength of a semi-rigid attachment structure 60 which will beformed from the first main yarns 62 for the first rigid fitting 50.

In step 706, second main yarns 62 are stitched through the openings 54of the second rigid fitting 50 and into the second flexible substrate 70with the embroidering machine. The embroidering machine is controlledaccording to a second computer numerical control process. The secondcomputer numerical control process may be selected according to adesired strength of a semi-rigid attachment structure 60 which will beformed from the second main yarns 62 for the second rigid fitting 50.The second computer numerical control process is different from thefirst computer numerical control process, and the strength of thesemi-rigid attachment structure 60 for the second rigid fitting 50 isdifferent from the strength of the semi-rigid attachment structure 60for the first rigid fitting 50.

In step 708, the first main yarns 62, the second main yarns 62, thefirst rigid fitting 50, and the second rigid fitting 50 are encapsulatedwith an encapsulant 66. The encapsulant 66 extends through the openings54 of the first rigid fitting 50 to form first fitting patch, andextends through the openings 54 of the second rigid fitting 50 to formsecond fitting patch. The encapsulant 66 is formulated at a temperaturewhich is lower than the melting point of the sheath of the first mainyarns 62 and the second main yarns 62.

FIGS. 8A-8B are detailed views of a fitting 50 for a fuel cell, inaccordance with some other embodiments. This embodiment is similar tothe embodiment of FIGS. 3A-3B, except the primer coating 56 is omitted.Manufacturing costs may thus be reduced.

Embodiments may achieve advantages. Forming the fuel cell 44 withflexible body 48 can make them more resistant to ballistic projectiles.Attaching a fitting 50 to a flexible body 48 with an attachmentstructure 60 that is semi-rigid can improve the reliability of themating point for the fuel cell 44, as the attachment structure 60 actsto buffer stress. Further, attaching a fitting 50 to a flexible body 48by stitching that is controlled with a CNC process allows the stitchingto be performed with greater precision and repeatability. Less yarns maybe used when attaching the fitting 50 to the flexible body 48, reducingthe weight of the resulting fuel cell 44, which may increase fuelefficiency of the rotorcraft 10.

Although described in the context of fuel cells, some embodiments may beutilized to attach other types of rigid fittings to other types offlexible substrates. For example, similar processes could be performedto attach cleats to a sponson. Likewise, a similar process could beperformed to embed smart hardware into tanks, sponsons, sonobuoys, orthe like.

Further, some embodiments contemplate use of the fittings 50 in otherapplications. Specifically, the fittings 50 may be used to attach a fuelcell 44 to other elements besides a rigid fuel line. As noted above,some of the fittings 50 may be utilized to fluidly couple multiple fuelcells 44 to one another. Likewise, other fuel cells 44 may have fittings50 that are reserved for adding fuel to or removing fuel from a fuelcell 44.

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications and combinations of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thedescription. It is therefore intended that the appended claims encompassany such modifications or embodiments.

What is claimed is:
 1. A method comprising: receiving a fittingcomprising openings extending through an outer portion of the fitting;placing the fitting on a flexible substrate; stitching main yarns intothe flexible substrate, the main yarns strung through the openings ofthe fitting; and encapsulating the main yarns and the outer portion ofthe fitting with an encapsulant, the encapsulant bonded to the flexiblesubstrate.
 2. The method of claim 1, further comprising: forming aprimer coating on the outer portion of the fitting, the encapsulantbonded to the primer coating.
 3. The method of claim 1, wherein theflexible substrate is formed of a first fuel-tolerant material and theencapsulant is formed of a second fuel-tolerant material.
 4. The methodof claim 1, further comprising: stitching support yarns into theflexible substrate and over the main yarns, the support yarns crossingthe main yarns.
 5. The method of claim 4, further comprising:encapsulating the support yarns with the encapsulant.
 6. The method ofclaim 1, wherein the main yarns are bicomponent yarns comprising a coreand a sheath.
 7. The method of claim 6, wherein the sheath has a meltingpoint, and the encapsulant is formed at a temperature which is lowerthan the melting point of the sheath.
 8. The method of claim 1, whereinstitching the main yarns into the flexible substrate comprises:threading bundles of the main yarns through respective ones of theopenings of the fitting, the main yarns of the bundles radiating fromthe openings.
 9. The method of claim 8, wherein the main yarns of thebundles curve in a same direction as the main yarns radiate from theopenings.
 10. A method comprising: receiving a fitting comprisingopenings extending through an outer portion of the fitting; placing thefitting on a fuel-tolerant substrate; forming an attachment structureby: programming a computer numerical control process according to astrength of the attachment structure; stitching yarns into thefuel-tolerant substrate with an embroidering machine, the embroideringmachine controlled using the computer numerical control process, theyarns strung through the openings of the fitting; and encapsulating theyarns and the outer portion of the fitting with an encapsulant.
 11. Themethod of claim 10, wherein the fuel-tolerant substrate is a flexiblesubstrate for a fuel cell fitting patch.
 12. The method of claim 10,wherein the fuel-tolerant substrate is a flexible body of a fuel cell.13. The method of claim 10, wherein programming the computer numericalcontrol process comprises: selecting a density, a length, and a radiusof curvature for the yarns.
 14. The method of claim 10, wherein theyarns each comprise a sheath having a melting point, and a moldingprocess for the encapsulant is performed at a temperature which is lowerthan the melting point of the sheath.
 15. A method comprising: placing afirst rigid fitting and a second rigid fitting on a first flexiblesubstrate and a second flexible substrate, respectively, the first rigidfitting comprising first openings extending through a first outerportion of the first fitting, the second rigid fitting comprising secondopenings extending through a second outer portion of the second fitting;stitching first yarns through the first openings and into the firstflexible substrate with an embroidering machine, the embroideringmachine controlled according to a first computer numerical controlprocess; stitching second yarns through the second openings and into thesecond flexible substrate with the embroidering machine, theembroidering machine controlled according to a second computer numericalcontrol process, the second computer numerical control process differentfrom the first computer numerical control process; and encapsulating thefirst yarns, the second yarns, the first rigid fitting, and the secondrigid fitting with an encapsulant, the encapsulant extending through thefirst openings and the second openings.
 16. The method of claim 15,wherein the first yarns form a first semi-rigid attachment structure forthe first rigid fitting, and the second yarns form a second semi-rigidattachment structure for the second rigid fitting, the method furthercomprising: selecting the first computer numerical control processaccording to a first strength of the first semi-rigid attachmentstructure; and selecting the second computer numerical control processaccording to a second strength of the second semi-rigid attachmentstructure, the second strength different from the first strength. 17.The method of claim 15, wherein the first rigid fitting and the firstflexible substrate form a first fitting patch, the second rigid fittingand the second flexible substrate form a second fitting patch, and themethod further comprises: attaching the first fitting patch to a firstside of a flexible fuel cell body; and attaching the second fittingpatch to a second side of the flexible fuel cell body.
 18. The method ofclaim 15, wherein the first rigid fitting is smaller than the secondrigid fitting.
 19. The method of claim 15 further comprising: forming afirst primer coating on the first outer portion of the first fitting;and forming a second primer coating on the second outer portion of thesecond fitting.
 20. The method of claim 19, wherein the first yarns andthe second yarns comprise a filament component having a melting point,the encapsulant comprises a polyurethane resin formulated fromisocyanate and polyol, and the polyurethane resin is formulated at atemperature lower than the melting point of the filament component.